Yes, you can just add the attachment and save it, @Agali.
Adding an attachment to a reconciled transaction won't affect your past reconciliations. You can also make other changes, but you'll have to be careful. These can unbalance your accounts and other reconciliations. It also affects the beginning balance of your next reconciliation. Make sure to review the previous one before doing so.
Additionally, if you reconciled a transaction by mistake, you have the option to unreconcile it.
I'm always around if you need any help with balancing your books. It's my pleasure to help. Have a good one.
